Solid-state imaging devices are used widely for video cameras, still cameras, and the like, and are provided in a form of a package in which an imaging element such as a CCD is mounted on a base made of an insulating material and a photo-detector region is covered with a transparent plate. In order to downsize the device, the imaging element is mounted on the base while keeping a bare chip state. As a conventional example of such a solid-state imaging device, a solid-state imaging device disclosed by JP 2001-77277 A is shown in FIG. 10.
In FIG. 10, 41 denotes a housing, which is composed of a base 41a and a frame-shaped rib 41b that are formed integrally by resin molding, above which an internal space 42 is formed. In the housing 41, a die pad 43 and leads 44 are embedded so as to be positioned at the center of the base 41a and under the rib 41b, respectively. An imaging element chip 45 disposed at the center of the internal space 42 is fixed to a top face of the die pad 43. Each lead 44 includes an internal terminal portion 44a that is exposed to the internal space 42 on a top face of the base 41a surrounded by the rib 41b, and an external terminal portion 44a that is exposed on a bottom face of the base 41a under the rib 41b. The internal terminal portion 44a and a bonding pad of the imaging element chip 45 are connected via a bonding wire 46 made of a metal wire. Further, a transparent sealing glass plate 47 is fixed to a top end face of the rib 41b, whereby a package for protecting the imaging element chip 45 is formed.
This solid-state imaging device is mounted on a circuit board, with a sealing glass plate 47 side facing upward, as shown in the drawing, and the external terminal portions 44b are used for connection with electrodes on the circuit board. Though not shown, above the sealing glass plate 47, a lens barrel incorporating an imaging optical system is to be attached, with the relative positional relationship of the same with a photo-detector region formed on the imaging element chip 45 being adjusted so that a predetermined accuracy is achieved. During an imaging operation, light from an object to be imaged is focused on the photo-detector region via the imaging optical system incorporated in the lens barrel, and is subjected to photoelectric conversion.
Since a solid-state imaging device with such a structure is connected with electrodes on a circuit board via its external terminal portions 44b exposed on the bottom face of the housing, the device has a small package height and a small occupied area and is suitable for high-density packaging as compared with a structure in which connection is achieved by employing outer leads that are bent downward from side faces of a housing.
For the resin molding of the housing 41 shown in FIG. 10, an upper mold 48 and a lower mold 49 as shown in FIG. 11 are used in the technique disclosed by JP 2001-77277 A. Atop face of the lower mold 49 is flat. On a bottom face of the upper mold 48, a recess 48a corresponding to the rib 41b is formed. On both sides of the recess 48a, an inner protrusion 48b for forming the internal space 42 and an outer protrusion 48c for forming external side faces of the rib 41b are provided, respectively. The leads 44 and the die pad 43, which are provided in a integrated state as a lead frame 50, are placed between the upper mold 48 and the lower mold 49.
The presence of the lead frame 50 between the upper mold 48 and the lower mold 49 causes a cavity 51 for molding the base 41a to be formed between the inner protrusion 48b of the upper mold 48 and the lower mold 49. A resin is filled therein in the foregoing state, and thereafter, the molds are opened and a molded article is taken out thereof. In the foregoing state of the molded article, the base 41a and the rib 41b composing the housing 41 has a finished shape. After the molding, from the lead frame 50, a portion thereof positioned outside the rib 41b is cut away.
In the foregoing conventional solid-state imaging device, a thickness of the internal terminal portion 44a of the lead 44 shown in FIG. 10 is approximately half a thickness of a portion thereof under the rib 41b, and a bottom face of the internal terminal portion 44a is not exposed on the bottom face of the base 41a. This shape of the lead 44 causes an inconvenience described below.
To embed the lead 44 at an appropriate position, a resin is filled, with the lead 44 being fixed between the upper and lower molds. For this purpose, the lead 44 has to be clamped between the upper mold 48 and the lower mold 49. However, as described above, the internal terminal portion 44a of the lead 44 positioned in the internal space 42 has a thickness such that the internal terminal portion 44a does not reach the bottom base of the base 41a, and hence, it is impossible to clamp the same between the upper and lower molds.
To cope with this, in the technique described in JP 2001-77277 A, each lead 44 is positioned by clamping a portion of the lead 44 on an outer side of its external terminal portion 44b between the outer protrusion 48c of the upper mold 48 and the lower mold 49. Consequently, the molding is conducted in a state in which the internal terminal portions 44a are not clamped between the upper and lower molds. Therefore, the process cannot achieve a state in which the inner protrusion 48b of the upper mold 48 is in close contact with the top faces of the internal terminal portions 44a with a sufficient pressing force. Therefore, resin burrs tend to occur along peripheries of the internal terminal portions 44a. The resin burrs thus having occurred narrow the contact areas on the internal terminal portions 44a significantly, and cause defects in the connection in some housings.
Next, a problem hindering the downsizing, which occurs in the foregoing configuration of the conventional example, is described below. As shown in FIG. 11, the outer protrusion 48c is needed on the external side of the rib 41b, in order to form the external side faces of the rib 41b using the outer protrusion 48c, whereby the outer shape of the rib 41b is completed upon completion of the resin molding. As a result, it is possible to clamp the lead 44 at the foregoing protrusion portion, while the following problem arises also.
In a housing in which the shape of the rib 41b is determined by the resin molding, an upper end face of the rib 41b as molded is required to have a sufficient width. The reason is that an area for application of an adhesive material for fixing the sealing glass plate 47 should be ensured on the upper end face. Therefore, the width of the upper end face of the rib 41b has a restricted lower limit. In other words, there is a limit on the reduction of the width of the rib 41b, which hinders the downsizing of the area for a semiconductor device. Further, in the housing where the rib 41b is molded, side faces of the rib need to be tapered for release from the mold, though the taper is not shown in the drawing. The taper also causes an increase in the width of the rib 41b. 